With the rapid development of technologies in networking and digital data storage, information and documents can be shared easily through a network system. For example, authorized research and development departments or institutes distributed all over the world may share and maintain their materials and efforts one another via the network system. FIG. 1 illustrates a network system including a data host 11 and a plurality of user hosts 12, 13, . . . , 1n interconnected via Internet 10. Documents 110 to be shared by the user hosts are stored in the data host 11 and accessible via Internet 10 to be acquired or updated.
As technological documents, unlike dictionaries, are generally complicated, it is hard to sort and index the contents of the technological documents simply by way of a text list or table of contents, and thus it is difficult for the users to search these contents efficiently. Aside from, if all the shared documents are stored in a single data host, it may suffer from limited transmission speed and risk losing data once the data host is damaged. Moreover, if the data host is unfortunately explored by a hacker, all the documents are likely to be stolen, which would be a serious problem for researchers.